The present invention relates to engine modeling and control and more particularly to a method of calibrating a direct injection stratified charge (DISC) engine.
Gasoline DISC engine technology has the potential of improving fuel economy through the use of stratified combustion, which significantly extends the lean burn limit and reduces pumping losses in the engine. Compared with a conventional port fuel injection (PFI) gasoline engine, a DISC engine is much more complicated in its hardware and operating strategy. Like a PFI engine, a DISC engine consists of an intake manifold, combustion chambers, and an exhaust system. Its hardware design and configuration, however, are different from a PFI engine in several key aspects. The location of injectors is different. In a DISC engine, fuel is injected directly into the cylinder as opposed to the intake port. The fueling system also differs. A high pressure fueling system is an important aspect of the DISC technology and is operated at a pressure that is 10-15 times higher than that of a PFI fueling system. The combustion chamber configuration of DISC engines also include non-flat piston heads having deliberately designed cavities to ensure charge stratification. The after-treatment package of a DISC engine typically requires the combination of a three-way catalyst (TWC) and a lean NOx trap (LNT) to meet emission standards.
With the special piston design and the high pressure fueling system, a DISC engine can effect two distinct modes of operation by properly timing the fuel injection in relation to other engine events. By injecting early in the intake stroke, there is enough time for the mixing of air and fuel to form a homogeneous charge by the time the ignition event is initiated. on the other hand, by injecting late in the compression stroke, the special combustion chamber design and the piston motion will lead to the formation of a stratified charge mixture that is overall very lean, but rich around the spark plug. In a typical DISC engine, a properly positioned swirl control valve can also contribute to enforcing the stratification in one mode and assuring good mixing in another.
The torque and emission characteristics corresponding to these two modes are so distinct that different strategies are required to optimize the engine performance in these different modes. Furthermore, in addition to the standard engine control variables such as throttle, fueling rate, spark timing and exhaust gas recirculation (EGR), other inputs, such as injection timing, fuel rail pressure and swirl control valve setting are also available.
The increased system complexity, coupled with more stringent fuel economy and emissions requirements, has made the DISC engine a control-intensive technology which depends heavily on the control system to deliver its expected benefits. Given the multitude of control inputs and performance indices, such as fuel consumption, emissions and other driveability measures, DISC engine control strategy development and system optimization rely heavily on model-based approaches and computer aided control design tools.
In particular, the development of calibration tables or engine maps for DISC engines is very time consuming. An engine sweep at a single engine speed/engine load operating point may require tens of thousands of steady-state mapping points. Each point requires stabilized engine conditions that may take several minutes to achieve. Thus, any hardware changes which result in the need to recalibrate the engine operating tables results in significant delay. Thus, there exists a need for alternative procedures that reduce the time and effort necessary to calibrate an engine strategy.
It is an object of the present invention to provide an improved method of calibrating a direct injection stratified charge engine.
The foregoing and other objects are attained by a method of calibrating a direct injection stratified charge (DISC) engine. The method comprises the steps of generating an estimated fueling rate map and torque map from engine steady-state mapping data, generating a transient engine operating trajectory along a predetermined parameter vector toward an associated desired torque, and iteratively modifying the estimated fueling rate map as a function of the generated torque resulting from the transient engine operating trajectory. In one aspect of the present method, the step of iteratively modifying the estimated fueling rate map includes updating the fueling map at each sampling time instant (tk) by applying a current estimated fueling rate associated with the estimated fueling rate map, and determining the engine torque value corresponding to the parameter vector. The torque value is then inverted to update the fueling map as a function of the engine torque value.
An advantage of the present invention is that it reduces the time to calibrate or map an engine torque strategy because calibration is performed with transient engine response data. The present invention also reduces calibration effort because the calibrator does not have to develop and identify detailed and accurate representation for the torque map and fueling map, as these are automatically generated during the course of the adaptation.
The present invention is also advantageous in that it increases the accuracy with which the desired torque is delivered.
Other objects and advantages of the invention will become apparent upon reading the following detailed description and appended claims, and upon reference to the accompanying drawings.